1. Field of the Invention
The present invention relates to vibration dampers particularly for use on engines or transmissions adapted to drive motor vehicles.
2. Related Art
Internal combustion engines experience torsional vibrations due to non uniform loading of the crankshaft from the cylinder pressure and the reciprocating parts of the engine. If the vibration becomes severe enough to damage the crankshaft or the accessories driven by the crankshaft, either the crankshaft must be redesigned or a method of controlling the vibration must be used. Elastomeric dampers may be used to reduce torsional, axial or bending vibration to an acceptable level. Elastomeric dampers behave like a combination of a tuned absorber and an energy dissipator. The tuning effect of the damper is achieved by the proper balance of elastomer stiffness and the inertia of the damper ring, while the energy dissipation is primarily determined by the inherent damping of the elastomer. Typically the damper may include a hub part adapted to be rigidly attached to the rotational shaft requiring damping, an outer inertia ring and an elastomeric material ring separating the ineretia ring from the hub part. An example of the foregoing type of vibrational damper is shown in Australian Patent Application No. 83399/87. Other examples are shown in Australian Patent Nos. 578170, 578846, 63868/86, 255913 and U.S. Pat. Nos. 1,944,233 and 4,710,152. There is also a growing tendency to drive vehicle accessories off the crankshaft of engines and when an elastomeric damper is mounted thereon, it is necessary to drive the accessories from the intertia ring of the damper. The foregoing would not apply where the shaft requiring balancing is in the transmission. This, to some extent has some disadvantageous effects on the performance of the damper.